1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a plasma display panel which can improve luminous efficiency while reducing a discharge firing voltage.
2. Discussion of the Background
In a plasma display panel (“PDP”), there is a three-electrode surface discharge type structure. The three-electrode surface discharge type structure includes substrate including sustain electrodes and scan electrodes which are formed on the same surface and another substrate which is spaced therefrom at a predetermined distance and has address electrodes arranged in perpendicular to the sustain electrodes and the scan electrodes. Also, a discharge gas is injected between the substrates. The discharge is determined by the discharge of the address electrodes and the scan electrodes which are connected to the lines, respectively, and are independently controlled, and the sustain discharge that displays a screen image by the sustain electrode and the scan electrode located on the same surface.
The PDP generates visible light using glow discharge, and several steps are performed from the step of generating glow discharge to the step in which visible light reaches the human eyes. That is, if the glow discharge is generated, plasma excited by collisions of electrons and gas is generated and then ultraviolet rays are generated from the excited plasma. Ultraviolet rays collide against a phosphor layer in a discharge cell to generate visible light and visible light passes through a transparent substrate to reach the eyes of a person. By these steps, an input energy applied to the sustain electrode and the scan electrode is significantly lost.
The glow discharge is generated by applying a voltage higher than a discharge firing voltage to two electrodes. That is, in order to initiate this discharge, a significantly high voltage is required. If the discharge is generated, a voltage distribution between an anode and a cathode is distorted by the space charge effect generated in a dielectric layer adjacent to the anode and the cathode. Formed between the electrodes are a cathode sheath region and an anode sheath region. The cathode sheath region adjacent the cathode consumes most of the voltage applied to the two electrodes for discharge. The anode sheath region adjacent the anode consumes another portion of the voltage. A positive column region formed between the anode and cathode regions barely consumes any of the voltage. In the cathode sheath region, electron heating efficiency depends on a secondary electron coefficient of an MgO protective film formed on the dielectric layer and, in the positive column region, most of the input energy is consumed for electron heating.
Vacuum ultraviolet rays for colliding against the phosphor layer and emitting visible light are generated when xenon (Xe) gas in an excitation state is transitioned to a ground state. The excitation state of Xe occurs by the collision of Xe gas and electrons. Accordingly, in order to increase a ratio of the input energy for generating visible light (that is, luminous efficiency), the collision of xenon (Xe) gas and the electrons must be increased. Also, in order to increase the collision of xenon (Xe) gas and the electrons, the electron heating efficiency must be increased.
In the cathode sheath region, most of the input energy is consumed and the electron heating efficiency is low, but, in the positive column region, the input energy is barely consumed and the electron heating efficiency is very high. Accordingly, by increasing the area or the length of the positive column region (discharge gap), high luminous efficiency can be obtained.
Moreover, it is known that, in the ratio of the electrons which are consumed according to a change in a ratio E/n of electric field E across the discharge gaps (positive column region) to gas density n, the electron consuming ratio in the same ratio E/n increases in the order of xenon excitation (Xe*), xenon ion (Xe+), neon excitation (Ne*), and neon ion (Ne+). Also, it is known that, in the same ratio E/n, the electron energy decreases as the partial pressure of xenon (Xe) increases. If the partial pressure of xenon (Xe) increases, the ratio of electrons which are consumed for exciting xenon (Xe) increases, among xenon excitation (Xe*), xenon ion (Xe+), neon excitation (Ne*), and neon ion (Ne+), thereby improving luminous efficiency.
As described above, increasing the area of the positive column region increases the electron heating efficiency. Also, the increasing of the xenon (Xe) partial pressure increases the electron heating ratio consumed for xenon excitation (Xe*) in the electrons. Accordingly, by increasing both the area and the length of the positive column region and the partial pressure of xenon (Xe) the electron heating efficiency increases and thus the luminous efficiency can be improved.
However, there is a problem in that the increasing the area or the length of the positive column region and the partial pressure of xenon (Xe) increases a discharge firing voltage and the cost of manufacturing the PDP.
Accordingly, to increase the luminous efficiency, the increase of the area or the length of positive column region and increase of the xenon (Xe) partial pressure needs to occur while maintaining a low discharge firing voltage.
For a given discharge gap distance and a given pressure, the discharge firing voltage required for a surface discharge structure is higher than the discharge firing voltage required for an opposed discharge structure.